In the manufacturing of wafer-level camera lenses, spacer wafers contain an array or pattern of spacer-wafer apertures. A liquid, such as a UV-curable polymer, is deposited into each aperture and is cast into an intermediate or final lens shape by a fabrication master, mold, or stamp. The casted polymer is then cured to form a solid lens.
In the casting step, excess polymer overflows from the spacer-wafer aperture, which can decrease production yields if not properly managed. One method of containing overflow material is to size the spacer-wafer aperture to span not only the lens diameter, but also a void region or overflow region between the fabrication master and the spacer wafer into which overflow material collects. Proper lens formation requires a minimum volume of material to be dispensed into the spacer-wafer aperture. Voids can ensure that the minimum volume is actually dispensed by containing excess dispensed material. However, by increasing the spacer-wafer aperture diameter, voids may limit the wafer die count—the number of die level cameras that can be manufactured per wafer assembly. Voids may also introduce stray light artifacts in the images the cameras form.
Precise control of polymer volume dispensed in each spacer-wafer aperture can also reduce yield loss caused by polymer overflow. However, the calibration and maintenance of such control adds to manufacturing costs.
In wafer-level optics manufacturing processes that employ suspended wafer-level optical elements, such as suspended lenses, high yield requires sufficient adhesion of each casted lens to its respective spacer-wafer aperture sidewall surface. A prior-art method to improve this surface adhesion includes applying a surface treatment to the spacer-wafer aperture sidewall.